The invention relates to a method of controlling a drive system in a motor vehicle having an electronic control device which determines a desired wheel torque from an accelerator pedal position.
Such a method is known, for example, from German Patent Document 196 37 210 A1. In the case of this known method, on the one hand, the wheel torque demanded by way of the accelerator pedal and, on the other hand, a conglomeration of various operating parameters are processed with one another in a central unit in a manner not shown in detail for controlling the drive system.
It is an object of the invention to improve a method of controlling a drive system in a motor vehicle with a view to optimizing comfort.
The invention is based on the following recognition:
By the method according to the invention, a control strategy for drive systems in motor vehicles in the event of insufficient friction conditions is to be created of a variable interpretation of the power control element (accelerator pedal). Here, the following state of the art is used as the basis: The spinning tendency or the wheel slip is conventionally sensed by stability regulating control devices (such as ESP, DSC) and is also transmitted as information to other control devices, particularly to engine control devices for controlling an internal-combustion engine and/or, as required, to transmission control devices for controlling automatic transmissions. In the event of the occurrence of slip, the engine control device first reduces the total wheel torque at the driven wheels by means of an intervention in the torque control of the internal-combustion engine or of the engine. As a rule, it is assumed in this case that the ratio of the transmission does not change during the regulating operation. Furthermore, transmission control devices are known which themselves react to the spin tendency of the driving wheels, in that, by changing the effective ratio, they reduce the total wheel torque until the determined wheel slip has been reduced. Finally, a wheel torque reduction can also be carried out by the braking system or by the stability regulating control devices.
The invention suggests an integrated approach in which the accelerator pedal is used as a power control element and, by way of its variable interpretation, to power output to the wheels is controlled such that occurring wheel slip is first reduced and is avoided during the subsequent regulating, in order to minimize the necessity of a complex coordination of a wheel torque control by several individual components.
It is assumed that the accelerator pedal is used as a power control element. The accelerator pedal position or the sensor signal value reflecting the accelerator pedal position therefore controls the power output or the torque output from the internal-combustion engine to the wheels. The wheel torque is obtained from the power supplied to the wheels minus the losses in the transmission line divided by the applied speed or velocity. The term wheel torque quantity should also be understood to be any quantity proportional to the wheel torque.
The signal emitted by the accelerator pedal proportionally to its position, is converted to a power demand or to a desired wheel torque in a characteristic curve or a characteristic diagram while additionally being a function of the speed and other parameters. The interrelationship between the input value and the output value of the characteristic curve or of the characteristic diagram can be dynamically corrected. In the following, these characteristic curves or characteristic diagrams will be called a basic characteristic curve in a summarizing fashion because, as a matter of priority, the invention relates to the dependence of the desired wheel torque on the accelerator pedal position. The characteristic curves according to the invention can therefore also be found in characteristic diagrams if the dependence on additional parameters is important.
The desired wheel torque or the demanded power is provided by the engine in the form of torque and pertaining rotational speed. In the transmission line, an automatic transmission provides that the rotational engine speed is adjusted which is required for the demanded power.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.